JPH06118344A - Polarization beam splitter module - Google Patents

Abstract

PURPOSE:To realize a function of two PBS modules by one PBS module. CONSTITUTION:The module is constituted of a polarization beam splitter 100, a collimator 116 for allowing a signal light from a signal mode fiber 110 for inputting the signal light to be made incident on the polarization beam splitter 100, a collimator 117 for allowing a local oscillation light from a polarization maintaining fiber 111 for inputting the local oscillation light to be made incident on the polarization beam splitter 100, collimators 118, 119 for condensing (x) axis direction polarization components of the signal light and the local oscillation light separated by the polarization beam splitter 100 to polarization maintaining fibers 112, 113 for an optical output, and collimators 121, 120 for condensing (y) axis direction polarization components of the signal light and the local oscillation light separated by the polarization beam splitter 100 to polarization maintaining fibers 115, 114 for an optical output.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarization beam splitter module used in a front optical circuit of a polarization diversity optical receiver in light wave (coherent) communication.

[0002]

2. Description of the Related Art FIG. 2 is a block diagram showing a configuration example of a conventional polarization diversity optical receiver.
l. 90, No. 316, IEICE (1990)
-11-20) p10.

The optical circuit of this polarization diversity optical receiver has a first polarization beam splitter (hereinafter referred to as PBS).
210 and the first polarization maintaining fiber (hereinafter referred to as PMF)
It is composed of a coupler 211, a first balanced receiver 212 with a polarization preserving coupler (hereinafter referred to as PMC), and a second balanced receiver 213 with PMC.

The first PBS 210 inputs signal light through a normal single mode fiber (hereinafter referred to as SMF) and outputs orthogonal polarizations to two output ports formed of PMF. The optical output fiber of the local oscillation light source 220 is a PMF and is fused to the input port PMF of the PMF coupler 211. The optical output of the local oscillation light source 220 is linearly polarized light, and its optical power is divided into two by the PMF coupler 211 and output by the two output port PMFs of the PMF coupler 211. First PBS 210 First
Output port and the first output port of the first PMF coupler 211 are input to the first balanced receiver 212 with PMC. On the other hand, the second output port of the first PBS 210 and the second output port of the first PMF coupler 211 are input to the second balanced receiver 213 with PMC.
The first balanced receiver 212 with PMC has PMC and D
It is composed of dual-PIN-photodiode and preamplifier IC, and two optical outputs of PMC are Dual-P.
IN-photodiode is optically coupled to two light receiving surfaces,
The intermediate frequency (IF) signal that is photoelectrically converted is Dual
-PIN-From the middle point of the photodiode, preamplifier IC
Is input to. Second balanced receiver with PMC 21
3 also has the same configuration and function. According to the above description, the components having the same polarization of the signal light and the local oscillation light are combined and detected in the balanced receivers 212 and 213 with PMC, and the IF signal corresponding to the polarization of the signal light is generated. You can get it. First balanced receiver with PMC 2
The first IF signal obtained at 12 is the first IF amplifier 21.
Amplified by 4 and the first differential detector 216 obtains a first baseband signal. Similarly, the second IF signal obtained by the second balanced receiver with PMC 213 also obtains the second baseband signal. The first baseband signal and the second baseband signal are added by the adder 218 to obtain the third baseband signal. The third baseband signal is independent of the polarization state of the signal light, and in this way a polarization diversity optical receiver is achieved.

Here, an automatic frequency control (AFC) circuit 219 changes the bias current of the local oscillation light source 220 so that the difference between the signal light frequency and the local oscillation frequency becomes constant in order to keep the center of the intermediate frequency constant. This is a circuit for changing the local oscillation frequency.

FIG. 3 is a configuration diagram showing another configuration example of a conventional polarization diversity optical receiver.

The optical circuit of this polarization diversity receiver uses a second PBS 221 instead of the first PMF coupler 211 shown in FIG. Second PBS 221
Has one input port and two output ports, and all optical fibers use PMF. By arranging the polarization main axis of the input PMF by rotating it by 45 degrees, the PBS 2
Obtain the bisected light output from 21. Others are the same as in the configuration example shown in FIG. 2, that is, they have the function of a polarization diversity optical receiver.

[0008]

However, any of the above-described optical circuits requires a large number of optical components, which causes a problem that the mounting space becomes large and the cost also becomes large.

An object of the present invention is, in order to eliminate the above problems, a first aspect of the optical circuit of a polarization diversity optical receiver.
PBS function and first PMF coupler (or second PMF
Both of the functions of BS) are realized by one PBS module.

[0010]

In order to achieve the above object, the present invention provides a polarization beam splitter for separating incident light into an x-axis direction polarization component and a y-axis direction polarization component, and an input signal light for the polarization beam splitter. The first port incident on
A second port for injecting the input local oscillation light into the polarization beam splitter, a third port for outputting a polarization component in the x-axis direction of the signal light separated by the polarization beam splitter, and a separation port for the polarization beam splitter A fourth port for outputting the polarization component of the local oscillation light in the x-axis direction, a fifth port for outputting the polarization component of the signal light separated by the polarization beam splitter in the y-axis direction, and a separation port for the polarization beam splitter And a sixth port for outputting the y-axis direction polarization component of the generated local oscillation light.

[0011]

The input signal light and the input local oscillation light which are respectively incident on the polarization beam splitter from the first port and the second port are separated into the x-axis direction polarization component and the y-axis direction polarization component, and the x-axis direction polarization component. The component is output to the outside from the third port and the fourth port, and the y-axis direction polarized component is output to the outside from the fifth port and the sixth port.

[0012]

1 is a block diagram showing a first embodiment of the present invention.

In FIG. 1, reference numeral 100 denotes a cube-shaped polarization beam splitter (PBS). For example, a polarization separation element made of a dielectric multilayer film is vapor-deposited on a triangular prism made of quartz glass, and the second triangular prism is used as an optical adhesive. It has been glued together. 110 is a single mode fiber for inputting a signal light. Reference numeral 111 is a polarization maintaining fiber for inputting locally oscillated light. Reference numerals 112 to 115 are polarization maintaining fibers for outputting light. Collimators 116 to 121 are composed of, for example, a ferrule, a lens, and a sleeve, and convert a light wave propagating from an optical fiber into a beam and output the beam, or collect a light wave propagating in a beam state into the optical fiber. Here, the ferrule has an optical fiber fixed to the center and the tip is obliquely polished, and the lens is, for example, a spherical lens having a diameter of 2.5 mm.

The above collimator 117 is arranged so that the principal axis of polarization of the emitted light wave has an inclination of 45 degrees with respect to the x axis shown in FIG. The collimator 118 and the collimator 119 are arranged so that, when a light wave having a polarization parallel to the x-axis shown in FIG. 1 is incident, the polarization main axes of the polarization-maintaining fiber 112 and the polarization-maintaining fiber 113 coincide with the polarization main axis of the light wave. It is located in. The collimator 120 and the collimator 121 are arranged so that, when a light wave having a polarization parallel to the y-axis shown in FIG. 1 is incident, the polarization main axes of the polarization maintaining fiber 114 and the polarization maintaining fiber 115 coincide with the polarization main axis of the light wave. It is located in.

Next, the operation of this embodiment will be described with reference to FIG.

The signal light propagating through the single mode fiber 110 is converted into a beam by the collimator 116 and is incident on the PBS 100. The x component of the polarization of the signal light incident on the PBS 100 goes straight on, enters the collimator 118, is condensed by the polarization maintaining fiber 112, and propagates through the polarization maintaining fiber 112. PBS
The polarization y component of the signal light incident on 100 is PBS.
At the center of 100, the traveling direction is changed to a right angle direction, the light enters the collimator 121, is condensed by the polarization maintaining fiber 115 and propagates through the polarization maintaining fiber 115. Here, since the signal light emitted from the collimator 116 has an arbitrary polarization state, the optical power ratio Sx: Sy of its x component and y component.
Takes any value.

On the other hand, the locally oscillated light which has propagated through the single mode fiber 111 is converted into a beam by the collimator 117 and is incident on the PBS 100. PBS100
The x-component of the polarization of the locally oscillated light that has been incident on the light beam advances straight as it is, enters the collimator 119, is condensed by the polarization maintaining fiber 113, and propagates through the polarization maintaining fiber 113. The y component of the polarization of the locally oscillated light incident on the PBS 100 changes its traveling direction at a right angle in the center of the PBS 100 and enters the collimator 120, and the polarization maintaining fiber 1
The light is focused on 14 and propagates through the polarization maintaining fiber 114. Here, since the locally oscillated light emitted from the collimator 117 is linearly polarized light having a polarization main axis of 45 degrees with respect to the x axis shown in FIG. 1, the optical power ratio L of its x component and y component is L.
x: Ly takes a value of 1: 1.

Thus, according to this embodiment, one PB
The S module can simultaneously realize the functions of the first PBS for the signal light and the second PBS for the local oscillation light.

FIG. 6 shows an example in which the PBS module according to the first embodiment described above is used in a polarization diversity optical receiver.

In FIG. 6, 140 is the PBS shown in FIG.
In the module, the polarization x component of the signal light and the polarization x component of the local oscillation light emitted from this PBS module are transmitted through the polarization maintaining fibers 112 and 113 shown in FIG.
The polarized light y component of the signal light and the polarized light y component of the local oscillation light guided to the first balanced receiver 212 with PMC shown in FIG.
Is guided to the second balanced receiver 213 with PMC. As a result, the polarization diversity optical receiver shown in FIG. 6 operates in the same manner as the conventional polarization diversity optical receiver shown in FIGS.

FIG. 4 is a block diagram showing a second embodiment of the present invention.

In the first embodiment shown in FIG. 1, when the polarization main axis of the local oscillation light emitted from the collimator 117 is deviated from 45 degrees with respect to the x-axis, the local oscillation is incident on the collimator 113 or the collimator 115. There is a problem in that the polarization component of light is reduced and reception sensitivity is degraded. Therefore, in this embodiment, as disclosed in detail in Japanese Patent Application No. 3-106292, the collimator 117 and PB shown in FIG.
By arranging the second PBS 101 as a polarizer during S100, the above problem is solved.

The second PBS 101 comprises two triangular prisms and a polarization main axis correcting means composed of a dielectric multilayer filter sandwiched between the two triangular prisms, and the polarization main axis is inclined by 45 degrees with respect to the x axis shown in FIG. Are placed at 45 degrees with respect to the x-axis.
100% of the linearly polarized light having the main axis of polarization is transmitted. According to this embodiment, it is possible to suppress the deterioration of the reception sensitivity due to the deviation of the polarization main axis of the input local oscillation light.

FIG. 5 is a block diagram showing the third embodiment of the present invention.

In this embodiment, the second PBS 101 shown in FIG. 5 is used.
Instead of this, the second PBS 102 and the 45-degree rotor 103 are arranged. The second PBS 102 has the same function as that of the second PBS 101, and is arranged so that polarized light parallel to the x-axis transmits 100%.
The degree rotator 103 is, for example, a half-wave plate. Also,
The collimator 117 is arranged so that the polarization axis of the emitted light wave is parallel to the x axis.

Therefore, the locally oscillated light emitted from the collimator 117 is transmitted through the second PBS 102 and the 45-degree rotator 1
It is converted into a direction rotated by 45 degrees with respect to the x-axis by 03, and enters the PBS 100. In this case, the same effect as that described in the second embodiment can be obtained.

In this way, both the second and third embodiments are applied to the polarization diversity optical receiver as in the first embodiment.

[0028]

As described above in detail, according to the present invention, since the functions of the two PBS modules described in the prior art are realized by one PBS module, the member cost, the manufacturing cost, and the optical cost can be reduced. The component mounting space can be significantly reduced. Therefore, the provision of a more practical polarization diversity optical receiver can be expected.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a first embodiment of the present invention.

FIG. 2 is a configuration diagram showing a conventional polarization diversity optical receiver.

FIG. 3 is a configuration diagram showing a conventional polarization diversity optical receiver.

FIG. 4 is a configuration diagram showing a second embodiment of the present invention.

FIG. 5 is a configuration diagram showing a third embodiment of the present invention.

FIG. 6 is a configuration diagram showing an embodiment of a polarization diversity optical receiver using a PBS module according to the present invention.

[Explanation of symbols]

 100 to 102 Polarizing beam splitter 103 45 degree rotator 110 Single mode fiber for signal light input 111 Polarization maintaining fiber for local oscillation light input 113 to 115 Polarization maintaining fiber for optical output 116 to 121 Collimator

Claims (3)

[Claims] 1. A polarization beam splitter that splits incident light into a polarization component in the x-axis direction and a polarization component in the y-axis direction, and a first beam splitter that inputs input signal light into the polarization beam splitter.
Port, an input local oscillation light is incident on the polarization beam splitter, a second port is output, the x-axis direction polarization component of the signal light separated by the polarization beam splitter is output, and the polarization beam X of the local oscillation light separated by the splitter
A fourth port for outputting an axial polarization component, a fifth port for outputting a y-axis polarization component of the signal light separated by the polarization beam splitter, and a local oscillation light separated by the polarization beam splitter And a sixth port for outputting a polarization component in the y-axis direction. 2. The polarization beam splitter module according to claim 1, further comprising a second polarization beam splitter provided between the second port and the polarization beam splitter. 3. The polarization beam splitter according to claim 1, further comprising a second polarization beam splitter and a 45-degree rotator provided between the second port and the polarization beam splitter.